A cement clinker, in the following referred to as a clinker, for short, is typically produced in a sintering process in so called rotary kilns. A clinker is discharged from the rotary kiln with a temperature of about 1450° C. onto an inlet distribution in the form of a bulk material bed, also known as a clinker bed. The clinker is then moved onto a grate cooler where it is cooled by cooling air and transported from the kiln to further processing stages, usually at first to a crusher. During this transport, a temperature exchange between hot clinker and cooling air takes place. The higher the resulting temperature of the cooling air, the more efficiently the contained heat can be reused as process heat in the kiln. Typical bed depths of the clinker bed are between about 0.4 m and about 0.8 m.
A typical grate cooler has at least one cooling grate having at least one support for the clinker. Cooling air is injected into said cooler via cooling air channels. The cooling air is used to transport the fine fraction of the bulk material bed upward allowing the cooling air to pass through the interstices between the larger particles undisturbed. This facilitates efficient cooling of the larger particles. Turmoil and stirring of the bulk material particles must be avoided, as this would result in a homogeneous temperature across the bed height. The desired bulk material bed temperature increases with the distance from the support, as the maximum cooling air temperature is governed by the temperature of the bulk material particles at the top of the material bed. Due to radiation losses at the surface, this optimum temperature profile cannot be realised, so the aim is to have the hottest section of the bulk material bed a few centimeters underneath the surface.
In order to achieve a uniform aeration, EP 0167 658 teaches a step grate having box-like grate elements, arranged in rows in parallel to each other, transversal to the conveying direction. The rear part of each row is overlapped by the front part of the preceding row (in conveying direction), thereby forming a structure resembling a stair, each step constituted by grate elements arranged side by side. Each grate element has several slot-like cooling air channels, arranged consecutively transversely to the conveying direction. The cooling air channels are constituted by gaps between grate segments, which are inserted in box-like carriers of the grate elements. The upper segments of the cooling air channels are straight and inclined in conveying direction, so that the cooling air exits the cooling air channels at an angle inclined in conveying direction and at least a noteworthy fraction of the cooling air flows along the support. The lower part of the slot-like cooling air channels is syphon-shaped, to prevent clinker from falling through the cooling air channels.
U.S. Pat. No. 8,132,520 discloses a grate cooler having multiple planks adjacently situated transverse to the direction of transport and operationally moved longitudinally relative to one another with moving gaps designed as blow openings situated therebetween. The planks form a grate floor. Cooling air is blown through the moving gaps into the bulk material on top of the planks. The upper parts of the moving gaps are straight and inclined in the direction of transport. The lower parts of the moving gaps are siphon-shaped.